Myelin of the peripheral nervous system (PNS) is a morphologically and functionally specialized membrane formed and maintained by Schwann cells. This membrane contains three major proteins (P0, P1, and P2) whose distribution within the sheath is not precisely known. Biochemical extraction of two of these myelin proteins (P1 and P2) results in extensive splitting and unraveling of the sheath along the major dense line. Recent morphological observations from freeze-fracture studies of the central and peripheral nervous systems indicate that both globular and elongated intramembraneous particles are evident on the membrane leaflets of the major dense line (P-faces). The objective of the proposed research is to use a morphometric approach to correlate the freeze-fracture and biochemical observations. Electrophoretic determinations of the amount and proportions of P1 and P2 proteins extracted from sciatic nerve myelin sheaths will be compared to the number and types of intramembranous particles seen in freeze-fracture preparations of normal and protein-extracted nerves. Morphological identification of the proteins represented by specific myelin intramembranous particles provides a sensitive and reliable tool to assay individual sheaths for the presence, density, and spatial distribution of these proteins. Thus, using the freeze-fracture technique, it will be possible to detail the sequence of membrane changes during myelinogenesis; it is expected that compaction and stabilization of the myelin sheath correlated with the appearance of P1 and/or P2 proteins in the membrane. Future studies will include the study of membrane changes during myelin breakdown and remyelination following nerve lesions.